The disclosures of the following priority applications are herein incorporated by reference:
Japanese Patent Application No. H11-031732
Japanese Patent Application No. H11-036047
Japanese Patent Application No. H11-036048
Japanese Patent Application No. H11-036049
Japanese Patent Application No. H11-036050
Japanese Patent Application No. H11-031733
Japanese Patent Application No. H11-040164
1. Field of Invention
The present invention relates to a wheeled work vehicle that travels on tires.
2. Description of Related Art
In order to improve the comfort of the operator driving a work vehicle travelling on tires such as a wheeled hydraulic excavator, which has come to run at an increasingly high speed in recent years, Japanese Laid-Open Patent Publication No.S 62-110509, Japanese Laid-Open Patent Publication No. H 6-278438, Japanese Laid-Open Patent Publication No. H 7-125523 and Japanese Laid-Open Patent Publication No. H 7-132723, for instance, each disclose a work vehicle having a suspension mechanism provided between the body and an axle.
In the work vehicle disclosed in Japanese Laid-Open Patent Publication No. S62-110509 (hereafter referred to as prior art 1), two sets of hydraulic cylinders are provided at the two sides, i.e., on the left side and the right side of the body, the upper ends of the cylinder tubes and the lower ends of the cylinder rods are respectively linked to the body and the beam provided over the axle by using pins, and a long hole extending along the vertical direction is formed at the center of the body to link the upper center of the beam and the center of the body with a pin inserted at the long hole. The head chambers of the left hydraulic cylinder and the right hydraulic cylinder are made to communicate with each other via a restrictor, the head chambers of the left and right hydraulic cylinders are also connected to an accumulator via a pressure control valve. The line between the pressure control valve and the accumulator is connected to a hydraulic pump via a check valve which allows hydraulic oil to flow toward the accumulator. As a result, while the body moves vertically due to the contraction of the hydraulic cylinders when the wheels are subject to strong impact during travelling, the load is damped since the pressure control valve opens to communicate the hydraulic cylinders to the accumulator. If either of the left wheel or the right wheel is subject to an impact, the pressure oil from one of the hydraulic cylinders flows into the other hydraulic cylinder to rock the body.
In the work vehicle disclosed in Japanese Laid-Open Patent Publication No. H 6-278438 or Japanese Laid-Open Patent Publication No. H 7-132723 (hereafter referred to as prior art 2), double-acting hydraulic cylinders are mounted at the right side surface and the left side surface of the body with head chambers of the hydraulic cylinders connected with each other via a piping. A restrictor and an accumulator are provided in the middle of the piping and the lower ends of the cylinder rods of the hydraulic cylinders are individually linked to the axle of the work vehicle with pins. Thus, the vibration of the axle occurring during travelling is absorbed and damped to improve the comfort of the operator while travelling the vehicle.
Japanese Laid-Open Patent Publication No. H 7-125523 discloses a work vehicle (hereafter referred to as prior art 3) achieved by linking the upper ends of the cylinder tubes of one set of hydraulic cylinders and the lower ends of the cylinder rods respectively to the center of the body and the center of the axle with pins and linking the center of the axle and either the left side or the right side of the body with a link. In this vehicle, the bottom chamber of the hydraulic cylinder is connected to an accumulator via a restrictor. As a result, while the body moves in the vertical direction due to the contraction of the hydraulic cylinders if the wheels are subject to a strong impact during travelling, the load on the hydraulic cylinder communicating with the accumulator is attenuated.
The work vehicles disclosed in the publications above present the following problems. Namely, in the work vehicle in prior art 1 having the body and the axle linked with each other through a pin, a load applied to the body and the axle along the forward/backward direction during an excavating operation or due to brakes applied on the travelling vehicle must be borne by the pin and, therefore, it is necessary to use a large pin having a large pin diameter to assure a sufficient degree of pin strength. In addition, the pin used to restrict the movement of the axle relative to the body slides along the vertical direction as the axle moves up and down, hastening the process in which the sliding area becomes worn. As a result, the play of the pin in the long hole increases, which causes a displacement of the axle relative to the body along the horizontal direction as well as along the vertical direction, thereby making it difficult to smoothly absorb an impact. Furthermore, since single-acting hydraulic cylinders are utilized, which are engaged only when they contract, an impact cannot be hydraulically absorbed while they are extended, allowing the impact to be applied to the component members.
Since the body and the axle are linked to each other by the left hydraulic cylinder and the right hydraulic cylinder in the work vehicle in prior art 2, an excessive load is applied to the hydraulic cylinders in the forward/backward direction and the lateral direction as well as along the vertical direction while the vehicle is engaged in an excavating operation or if the vehicle is rocked.
In the work vehicle in prior art 3, since the body and the axle are linked to each other through the central hydraulic cylinder and the link, there is no means for limiting the rocking movement of the body, and thus, a shock related to the rocking movement cannot be absorbed. Thus, the work vehicle disclosed in the publication, in which the frame is not allowed to move vertically or to rock in a smooth manner while absorbing any impact from the axle, is not suited for practical use.
The work vehicles in prior art 2 and prior art 3 also present a problem in that while a fixed restrictor is provided in the passage between the hydraulic cylinder and the accumulator, the bottom chamber and the rod chamber of the hydraulic cylinder are not made to communicate with each other, which allows the attenuating force of the suspension to entirely depend upon the size of the sectional area of the variable constriction, thereby presenting difficulty in satisfying the personal preferences of individual operators.
Furthermore, since the movement of the left hydraulic cylinder and the right hydraulic cylinder are adjusted by a single accumulator in the work vehicles in prior art 1 through prior art 3, the capacity of the accumulator is bound to be large, which necessitates the scale of the accumulator to be large as well. It is difficult to fit such a large accumulator within the limited space inside the body through efficient space utilization, which places limits on the degree of flexibility with regard to wheeled hydraulic excavator design. In particular, if a bladder-type hydro-pneumatic accumulator is to be utilized, its structure necessitates that it be installed vertically, placing further restrictions on the installation arrangement. As a result, the accumulator may need to be installed with a part thereof projecting out from the body and, in such a case, a falling object or the like may collide with the projecting portion to damage the accumulator.
The work vehicle in prior art 2 is provided with a spool-type three ports/three positions solenoid control valve for leveling the height of the vehicle. By switching this solenoid control valve, the pressures in the hydraulic cylinders are controlled so as to set the distance between the axle and the body while the vehicle travels or it is engaged in operation to a predetermined specific value, to level the height of the vehicle.
However, since the suspension performance is effected while controlling the pressure at the hydraulic cylinder while the vehicle travels, it is difficult to correctly set the various parts (such as the restrictor) that affect the suspension performance in the work vehicle in prior art 2. In addition, since the pressures at the hydraulic cylinders are controlled during operation as well, the suspension is soft, which may cause the operator some discomfort.
Furthermore, a spool-type solenoid control valve is utilized in the work vehicle in prior art 2, and the solenoid control valve is switched to the neutral position to cut off the hydraulic cylinders from the hydraulic source or the tank when it is not necessary to level the height of the vehicle such as when the vehicle travels. However, since spool-type control valves tend to readily allow leaks at the neutral position, there is a concern that the vehicle height may change while the vehicle travels or while it is in a stationary state.
The vehicle height is leveled primarily to sustain a specific standard vehicle attitude when the weight balance between the front and the rear of the vehicle changes (e.g., the body leans forward) due to a front attachment replacement. Accordingly, the vehicle should be leveled through an operation performed outside the cabin while visually checking any change occurring in the vehicle attitude and, as a result, the height of vehicle cannot be fine-tuned through an operation performed within the cabin with ease.
However, if an operating lever to be used to operate a leveling control valve is provided outside the cabin in order to achieve leveling through an operation of the operating lever, the operating lever may be inadvertently turned due to an impact from the road surface even when the vehicle is not being leveled such as while it is travelling, to accidentally switch the control valve to a position other than the neutral position. This will result in undesirable fluctuation in the vehicle height.
Moreover, if the operating lever to be used to operate the leveling control valve is provided outside the cabin, the operability is compromised and the operating lever may even be damaged by an object falling from the front. In addition, when the suspension circuit is formed by switching the leveling control valve to the neutral position, it is necessary to take into consideration the positional relationship between the control valve and the accumulator in order to obtain the maximum suspension performance (in particular, the maximum accumulator performance) since the distance from the control valve to the accumulator affects the suspension performance.
An object of the present invention is to provide a wheeled work vehicle capable of effectively absorbing an impact occurring while the vehicle is travelling.
In order to achieve the object described above, the wheeled work vehicle according to the present invention comprises a link that links at least one of axles provided at the front and the rear of the vehicle to the chassis, suspension hydraulic cylinders provided on the left and right sides of the chassis, which connect the axle to the chassis in conjunction with the link and an accumulator that is allowed to communicate with the oil chambers of the hydraulic cylinders via restrictors.
This structure allows the axle to smoothly move along the vertical direction and also to smoothly rock relative to the frame to enable efficient absorption of a shock occurring when the hydraulic cylinders expand/contract, to facilitate the adoption of the work vehicle in practical use.
The work vehicle according to the present invention may further comprise a means for adjustment that changes the suspension performance in correspondence to the area of the passages communicating between the bottom chambers and the rod chambers of the hydraulic cylinders. By providing such a means for adjustment, the suspension performance, in particular the damping performance can be changed with ease.
The work vehicle may further comprise a means for adjustment that changes the suspension performance in correspondence to the area of the passages communicating between the hydraulic cylinders and the accumulator. By providing such a means for adjustment, the suspension performance and, in particular, the damping performance can be adjusted with ease.
It is desirable to use a diaphragm-type accumulator that separates the internal gas and the oil through a diaphragm and to install the accumulator in the space formed by the frame without any parts of the accumulator projecting out from the upper end surface and the lower end surface of the chassis. The accumulator thus installed within the limited space with a high degree of efficiency is protected from falling objects and the like.
The wheeled work vehicle according to the present invention may comprise a hydraulic source from which pressure oil originates, a supply/discharge device that expands/contracts the hydraulic cylinders by supplying the pressure oil to the hydraulic cylinders and discharging the pressure oil from the hydraulic cylinders, a traveling-state detection device that detects whether the vehicle is in a travelling state or in a non-travelling state and a leveling/suspension switching device that allows the supply/discharge device to expand/contract the hydraulic cylinders when the traveling-state detection device detects that the vehicle is in a non-travelling state and prohibits the expansion/contraction of the hydraulic cylinders by the supply/discharge device if the traveling-state detection device detects that the vehicle is in a travelling state to engage a suspension function.
This eliminates the necessity for taking into consideration the requirements that must be met to realize a leveling function when designing the suspension performance to be achieved while the vehicle travels, to facilitate settings to be made at the various components involved in achieving the suspension performance.
Alternatively, it is desirable that the wheeled work vehicle according to the present invention further comprise a hydraulic source from which pressure oil originates and a leveling valve that switches the oil supply/discharge path to/from the hydraulic cylinders during a leveling operation in response to an operation of an operating lever, with the operating lever projecting out from a side surface of the chassis further toward the front of the vehicle relative to the axle.
This improves the operability during a leveling operation since the operator does not need to insert his hand into the recessed part so as to operate the operating lever, and also it allows the operator to visually check for any positional changes occurring with regard to the positions of the hydraulic cylinders and the link connecting the body to the axle to enable a highly reliable leveling operation to be performed with ease.
As a further alternative, the wheeled work vehicle according to the present invention may further comprise a hydraulic source from which pressure oil originates, a leveling valve that switches the oil supply/discharge path to/from the hydraulic cylinders during a leveling operation and a stop valve that disconnects the supply/discharge path from the hydraulic cylinders.
By adopting the structure described above, the quantity of oil that is leaked from the hydraulic cylinder is minimized, to prevent the upper swiveling body from being lowered to an undesirable extent.
It may be further provided with a retaining member that is utilized to operate the stop valve at the travelling body and to retain the stop valve at the cutoff position. Such a retaining member retains the stop valve at the cutoff position even if an external impact is applied when the stop valve is switched to the cutoff position to minimize the leak from the hydraulic cylinders reliably.